Browsing by Author "Sanford, William E., advisor"

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Open Access
Comparison of alternative estimators of deep percolation in full and deficit irrigation
(Colorado State University. Libraries, 2015) King, Jonathan, author; Sanford, William E., advisor; Butters, Gregory, committee member; Ronayne, Michael, committee member
Farmers are increasingly selling their water rights to growing municipalities and abandoning their farms (buy and dry). A loss of food production in the midst of a growing population is a recipe for food shortages. There is a need for municipalities to meet their water demand from the water rights held by farmers while farmers continue to produce crops. One solution to prevent a 'buy and dry' scenario is for farmers to lease a portion of their water rights to municipalities and continuing to farm under a deficit irrigation program. For this solution to work Colorado Water Law requires that return flows be maintained for down gradient water users. According to Colorado Water Law, deep percolation is any water in the unsaturated zone below the root zone (Colorado Foundation for Water Education, 2009). Deep percolation is also assumed to result in groundwater recharge. The first objective of this study is to quantify deep percolation. The second objective is to determine an optimal deficit irrigation technique. The third objective is to evaluate the methods used to estimate deep percolation. This study investigated three different cornfields (referred to as Blocks) in 2011 in Greeley, Colorado. Each block practices different flood irrigation techniques for the purpose of finding an optimal deficit irrigation plan. Block 2 practices traditional flood irrigation, Block 1 applies water at the same frequency as in Block 2 but uses half the volume of water, and Block 3 only irrigates twice during the growing season but applies large volumes of water per irrigation. Three methods were used to estimate deep percolation in each block: Lysimeters, Unsaturated Zone Water Balance (UZWB), and Darcy Flux. At the same time as this study, the United States Department of Agriculture - Agricultural Research Service (USDA-ARS) estimated deep percolation using a water balance method. The lysimeter method found an average deep percolation for Block 1 at 58mm, Block 2 at 334 mm, and Block 3 at 238 mm. The UZWB method found an average deep percolation for Block 1 at 291mm, Block 2 at 518 mm, and Block 3 at 516 mm. The Darcy flux method found an average deep percolation for Block 1 at 209 mm, Block 2 at 160 mm, and Block 3 at 1,246 mm. The USDA-ARS found an average deep percolation for Block 1 at 391 mm, Block 2 at 838 mm, and Block 3 at 635 mm. Corn was harvested by the USDA-ARS at the end of the season and yields were estimated. Block 1 produced 149 bushels/acre, Block 2 produced 196 bushels/acre, and Block 3 produced 84 bushels/acre. All methods found the irrigation strategy applied to Block 3, in relation to the other Blocks, resulted in the greatest percentage of deep percolation compared to water applied. The lysimeter method determined that the irrigation plan used in Block 1 was the least efficient in creating deep percolation while the UZWB and Darcy Flux method found that the irrigation applied to Block 2 was the least efficient. Although Block 3 was the most effective in producing deep percolation it produced the least amount of corn. The UZWB method was thought to be the most valuable method in this study. Installation of the neutron probe access tubes caused minimal disturbance to the soils and this method investigated the entire unsaturated zone below the zero flux plane, which accounted for most vertical heterogeneity. The lysimeter method was the most direct method, but installation caused extensive soil disturbances. However, once the soil settled over time the lysimeter method provided consistent and reliable results. In this study the Darcy Flux Method provided the greatest range in results compared to the other methods. The primary concern in using the estimates from this method was the quality of the data collected by the sensors.
Open Access
Fluorescent nanosphere transport: groundwater tracing and implications for nanoparticle migration through groundwater systems
(Colorado State University. Libraries, 2015) King, Charlene N., author; Sanford, William E., advisor; Li, Yan Vivian, advisor; Ronayne, Michael J., committee member; Sale, Thomas, committee member
Engineered nanoparticles (NPs) are being introduced to water supplies and many NPs have been shown to have deleterious effects on plants and animals; however, their behavior in natural substrates is not well characterized. In an effort to characterize nanoparticle migration through porous media a dual-tracer of fluorescent carbon nanospheres (CNP) and bromide (Br) were deployed through columns of porous media designed to be homogeneous, have dual-porosity, or be reactive. The CNP are hydrophilic, non-toxic, inert, and only 5 to 10 nm in diameter. Unlike other colloid tracers CNP are designed to be inexpensive, easy to identify, and not susceptible to pore throat filtering or settling making them an ideal particle tracer. The results of the homogeneous tests show that CNP and Br had identical breakthrough curves with retardation factors close to 1, confirming that CNP transport conservatively through silica sand. The results of the dual-porosity tests suggested that CNP may undergo slightly less transverse diffusion (mass transfer) into the immobile zone than the solute tracer Br. However the differences were less than expected because molecular diffusion was overwhelmed by the high pore velocities in the experiments. The results of the reactive media tests showed that in columns with surface-modified zeolite (SMZ) the CNP transported conservatively, while Br had a retardation factor 11 to 18 times higher, due to sorption. This means that the CNP can function as the conservative species used in a multiple tracer test to quantify the surface area exposure of other minerals or contaminants with a surface charge along preferential flow paths. During each of these experiments the average mass recovery for CNP was 95% indicating that there was minimal mass loss from pore throat filtering, settling, or sorption. Not only are CNP an extremely useful new tracer for groundwater systems, but they also provide insight as to how other NPs might be transported once introduced into the subsurface. NPs with surfaces that have been functionalized to be hydrophobic or preferentially sorb to a target constituent behave differently. If NPs which sorb to a particular contaminant are introduced to the subsurface it could facilitate transport of that contaminant or facilitate sorption. Similarly the rapid transport properties of hydrophilic NPs should be considered where any toxic NP is being introduced to natural systems.
Embargo
Identifying seepage pathways through an embankment dam using electrical and electromagnetic geophysical methods
(Colorado State University. Libraries, 2024) Warden, Camilla, author; Sanford, William E., advisor; McGrath, Daniel, committee member; Bailey, Ryan T., committee member
In the 1950's, increased water supply demands resulted in a construction project at the earth and rockfill embankment Little Wood River Dam to increase the reservoir water capacity. After the enlargement of the structure from 1958 to 1960, seepage was observed in the auxiliary spillway channel, vicinity of the downstream toe, and downstream on river left. In earth and rockfill embankment dams, seepage can manifest as internal erosion, or "piping", which may compromise the structural integrity of the embankment over time. Though no symptoms of internal erosion were observed, seepage monitoring weirs reported a significant increase in seepage flow rate when the reservoir surpasses a particular "critical" elevation or was at high pool conditions. As a result, the United States Bureau of Reclamation, the operator of the dam, opted to do a comprehensive site review to identify potential seepage pathways and determine if remediation were necessary. This geophysical study was designed to compare survey results to see if there was a change in subsurface saturation from low to high pool, that may indicate the presence of a seepage pathway originating at the reservoir. Additionally, this investigation also explored the groundwater conditions at the study area to determine if regional groundwater flow was contributing to observed seepage. Electrical and electromagnetic near-surface geophysical surveys were conducted in September 2021 (low pool) and June 2023 (high pool) and compared as timelapse to show any changes in subsurface bulk electrical resistivity distribution that could be attributed to change in moisture content or a seepage pathway that becomes active due to the increased hydraulic gradient from high pool reservoir conditions. Repeated Electrical Resistivity Tomography and Frequency Domain Electromagnetic surveys were conducted during low and high pool, and a Streaming Potential survey and Saltwater Injection Tracer Test were conducted during high pool only. Findings revealed that seepage originating at the reservoir travels through the left abutment and main embankment through a discontinuity between the dam enlargement material and underlying unit. Seepage from the reservoir contributes to the seepage seen in the auxiliary spillway channel and in the vicinity of the downstream toe. Regional groundwater flow from outside the reservoir footprint also contributes to observed seepage in the auxiliary spillway channel, vicinity of the downstream toe, and downstream on river left. Results of this geophysical study allowed for the delineation of seepage pathways through the left abutment and main embankment, providing a valuable contribution to the larger comprehensive review that will determine if future work to the structure is necessary. Regional groundwater was found to be a contributor to all observed seepage which may result in the extension or installation of concrete cutoff walls designed to prevent flow. Locations of observed seepage pathways can be individually targeted for remediation such as trenching and backfilling with impervious materials, and other observed seepage zones can be strategically monitored and maintained. Increasing the timelapse survey coverage to include average water level conditions could further improve the results and delineate if seepage observed below the critical elevation were being contributed to solely by groundwater flow. This timelapse technique paired with multiple electrical and electromagnetic geophysical methods provided extensive data coverage and excellent data quality that could be utilized for similar seepage studies.
Open Access
Low-cost data loggers for use with the conductivity mass balance method to estimate baseflow at snowmelt-dominated headwater streams in northwestern Colorado
(Colorado State University. Libraries, 2021) Lidell, Amber Leigh, author; Sanford, William E., advisor; McGrath, Daniel, committee member; Covino, Tim, committee member
Groundwater contribution to streamflow (baseflow) in snowmelt-dominated headwater streams, particularly following the snowmelt peak, is crucial for sustaining late season flow necessary for maintaining instream functions and fluvial ecosystems. Quantification of baseflow following snowmelt helps managers to determine the potential impacts of climate variability or management activities on streamflow, among others. One method of estimating baseflow is the conductivity mass balance (CMB), which requires continuous measurement of stream discharge and specific conductance (SC). Most headwater streams lack this information, as commonly used data loggers to measure SC are costly, and headwater streams have extreme variations in accessibility, temperature, discharge, and sediment. The purpose of this study is to investigate a new means to log continuous SC data in snowmelt-dominated headwater streams where data collection options are limited by costs. The primary objectives include deploying, calibrating, and testing a new low-cost data logger to continuously measure SC, gauging ungauged streams to determine continuous discharge, and estimating baseflow. The low-cost Stream Temperature, Intermittency, and Conductivity (STIC) data loggers were developed by modifying Onset HOBO Pendant waterproof temperature and light data loggers. 17 of these loggers as well as three higher-cost SC loggers were deployed in 10 streams in the Medicine Bow-Routt National Forests in northwestern Colorado in 2017 and/or 2018. Nine headwater streams were gauged, and rating curves developed to determine continuous discharge. 15 STIC loggers were then calibrated to known SC standards, and of those, in-stream data from 11 were used with discharge data to estimate baseflow at seven sites. Regression outputs for these 11 are available in the supplementary files. The conductivity-discharge relationships of two streams did not meet the requirements of the CMB method. Baseflow was also estimated at two streams with data from the higher-cost SC loggers. During the 2018 post snowmelt-dominated period, the data from STIC and higher-cost loggers recorded data that were used to calculate a proportion of baseflow to total streamflow (baseflow index) within 0.7 percent of one another at North Fork of the Elk River. Data from two STIC loggers that were deployed at Roaring Fork of Slater Creek were used to estimate baseflow indexes within 0.2 percent of one another. The data recorded by STIC loggers worked well with discharge data to estimate baseflow at seven sites with the CMB method during the post snowmelt-dominated portion of each hydrograph, even after being subjected to extreme field conditions. Once calibration and data processing time were taken into account, seven STIC loggers can be used for approximately the same cost as one higher-cost SC logger. For the best STIC logger data acquisition, it is recommended to deploy two low-cost loggers at each site as was done for this study, in a location that is not likely to experience heavy deposition, extremely turbulent flows, or long-term frozen water (e.g., in a glide or near a pool-tail crest). It is also recommended to calibrate the STIC loggers prior to field deployment, as was not done in this study. The findings of this study encourage the possibility of collecting more continuous data at more snowmelt-dominated headwater streams due to the low cost of these STIC loggers. This in turn increases potential for more baseflow data to be acquired at these streams, to inform and support public land and water management decisions and add to the active area of research surrounding baseflow estimation at headwater streams.
Open Access
Numerical modeling and hydrochemical analysis of the current and future state of seawater intrusion in the Todos Santos aquifer, Mexico
(Colorado State University. Libraries, 2019) Fichera, Marissa M., author; Sanford, William E., advisor; Ronayne, Michael J., committee member; Bailey, Ryan T., committee member
The Todos Santos aquifer, Baja California Sur, Mexico, provides the sole source of freshwater to the town of Todos Santos, and is utilized for domestic and agricultural needs crucial to the town's economy. The region is characterized by an arid climate. Major recharge to the aquifer is supplied from intermittent cyclones. Irregular and unpredictable recharge rates combined with population growth resulting from resort development put the Todos Santos aquifer at risk of overexploitation, causing potentially permanent water quality degradation by salinization as a result of seawater intrusion. Understanding the complex response of seawater intrusion to variable pumping rates and sea-level rise is critical to water resource management in Todos Santos. This study utilized numerical simulation of variable-density groundwater flow, using SEAWAT, in conjunction with temporal and spatial hydrochemical analysis, to evaluate the current and future extent of seawater intrusion in the area. Forecasting simulations were run for five, ten, and twenty years following 2017, for five different hydrologic scenarios, which implemented various pumping rates, sea-level rise, and overexploitation of significant surface water resources. Hydrochemical analysis shows an increase in groundwater specific conductance and chloride concentration within two kilometers of the coastline from 2007 to 2017. This combined with the distribution of groundwater samples exhibiting chloride concentration above the permissible limit for potable water (250 mg/L) suggest that the Todos Santos aquifer is experiencing effects of seawater intrusion up to 1.6 kilometers inland as of 2017. Analysis of groundwater cation exchange reactions indicates widening of the freshwater-seawater mixing zone from 2007 to 2017, further suggesting the exacerbation of seawater intrusion over this time span. Forecasting simulation results indicate that the extent of seawater intrusion is exacerbated by increased water withdrawal, overexploitation of surface water resources, the current rate of sea-level rise (~ 4 mm/yr), and an increased rate of sea-level rise of 25 mm/yr.
Open Access
Stable isotope (δ2H and δ18O) characterization of the South Platte River, Colorado
(Colorado State University. Libraries, 2011) Dávila-Olmo, Katherine, author; Sanford, William E., advisor; Stednick, John D., committee member; Ronayne, Michael, committee member
Stable isotope compositions (δ2H and δ18O) were examined at 13 sites along the South Platte River, Colorado during the water year 2009-2010. As a natural part of the water molecule, stable isotope (δ2H and δ18O) compositions are used as indicators to trace flow of water in the hydrologic cycle, allowing the identification of sources of water and evaporation processes. A strong positive correlation was determined between δ2H and δ18O compositions along the South Platte River, from Henderson to Julesburg, CO. All isotope compositions plotted below the global and regional meteoric water lines, indicating these were enriched in the heavy isotope forms relative to precipitation. Isotopic compositions were observed to vary spatially and temporally and between low and high flows. Mean isotope compositions became enriched with distance downstream from Henderson (-110.2 ‰ δ2H and -14.4 ‰ δ18O) to Julesburg (-94.5 ‰ δ2H and -12.0 ‰ δ18O). Mean isotope compositions also varied during different seasonal periods, with enriched compositions in the fall (September and October) (-98.9 ‰ δ2H and -12.5 ‰ δ18O) and winter (January and February) (-100.7 ‰ δ2H and -12.5 ‰ δ18O) seasons of 2009-2010 relative to those during the summer (June and July) (-104.8 ‰ δ2H and -13.5 ‰ δ18O) of 2009 and the spring (April and May) (-102.8 ‰ δ2H and -13.6 ‰ δ18O) and summer (June) (-114.1 ‰ δ2H and -15.2 ‰ δ18O) seasons of 2010. Furthermore, mean stable isotope compositions were generally enriched during the low flow (-99.5 ‰ δ2H and -12.8 ‰ δ18O) period from July 2009 to April 2010 relative to the high flow (-110.1 ‰ δ2H and -14.3 ‰ δ18O) period in June 2009, May and June 2010. The observed enrichment and changes in isotope compositions could have been due to: 1) the contribution to river discharge of different sources of water characterized by particular isotope signatures 2) evaporation processes where lighter isotope forms are favorably transformed to the vapor phase, concentrating the heavier isotope forms in the liquid phase 3) a change of origin of vapor sources with varying isotope signatures during different seasons and 4) a combination of the above.
Open Access
Water quality changes at a streamflow augmentation project, Lower South Platte River, Colorado
(Colorado State University. Libraries, 2003) Watt, Jamey T., author; Durnford, Deanna S., advisor; Sanford, William E., advisor; Stednick, John D., committee member
Flow augmentation projects utilizing managed groundwater recharge serve as a management tool for the conjunctive use of groundwater and surface water. The projects emphasize providing adequate water quantity at the right place and at the right time. However, water quality must be addressed. Mixing of different qualities within such a system can affect water quality both in the river and in the alluvial aquifer. The Tamarack Ranch Groundwater Recharge Project (Project) operates adjacent to the South Platte River in northeastern Colorado. The Project re-times excess flows in the South Platte River using managed groundwater recharge. Surface water, groundwater, and extraction water samples from the site were analyzed for water quality parameters and ionic composition. Water chemistry from the different sample locations determined the spatial and temporal influence of managed recharge activities. Two primary and distinct source waters are present in the system – groundwater and river water. The groundwater is dominated by calcium and bicarbonate. The river water is dominated by sodium / calcium and sulfate. The extraction water is a mixture of these two sources. The application of a simple batch mixing technique determined that the extraction water was about 80% groundwater. This research found that a streamflow augmentation project using managed groundwater recharge does affect water quality. As the system continues to operate, alluvial aquifer water quality will be affected by the surface water quality. A space for time substitution shows how groundwater quality is changing due to the effects of additional river water entering the alluvial aquifer system.